Examining Downstream Impacts of Mesoscale Sea Surface Temperature Anomalies on Trade Cumulus Clouds in Satellite Observations

Trade-wind cumuli play a key role in the earth’s radiative budget and are at the heart of the longstanding uncertainty in climate sensitivity estimates. Understanding the mesoscale spatial organization (20 to 2000 km) of trade cumuli is at the forefront of addressing this uncertainty. Recent observations have shown that trade cumulus cloudiness is locally modulated by the weak yet ubiquitous sea surface temperature anomalies (SSTAs) over O(10-100) km in the Northwest Tropical Atlantic trade wind region. Specifically, the daily cloud fraction is increased above daily warm SSTAs. We hypothesize that the associated condensation heating anomalies can trigger convective aggregation downwind of warm SSTAs through an inherent convective instability for nonprecipitating shallow cumulus shown in Janssens et al. 2023. To test this hypothesis, we employ a Lagrangian framework where trade cumulus trajectories are estimated using ERA5 wind fields at 925 hPa. These Lagrangian cloud trajectories are initiated over the daily centroids of warm and cold mesoscale SST anomalies identified from the NOAA GOES-POES blended SST analysis at different local times. Cloud properties and cloud organization metrics are obtained and computed from the NASA SatCORPS CERES GEO Edition 4 GOES-16 Northern Hemisphere V1.2 product. Our preliminary composite analysis on ~400 Lagrangian trajectories passing warm and cold SSTAs, respectively, in the EUREC4A/ATOMIC region suggests that there is likely a downstream response in trade cumulus cloud fraction within 6 hours (~170 km) after an air parcel passes through a warm or cold SSTA. For trajectories initiated over the daily centers of SSTAs at 1:30am LT, we found that cloud fraction reduces after experiencing warm SSTAs and increases after experiencing cold SSTAs, similar to stratocumulus cloud responses to large-scale SST perturbations. The outcome of this study will help clarify the role of mesoscale air-sea interaction in trade cumulus cloud organization.